Field of the Invention
The present invention relates to a nano-catalyst and preparation method thereof, and in particular, to a highly active iodine-doped TiO2 nano-catalyst and preparation method thereof, as well as use thereof in transformation of trans-carotenoids into their cis-isomers, which belongs to the field of production of inorganic nano catalytic materials and health food.
Description of Related Art
Carotenoids are a class of compounds having special physiological functions and pharmacological functions and are important on human health. Because of the effects of steric hindrance by methylation, the conjugated double bond in the molecule cannot rotate freely, carotenoids may have many stereoisomers. But, in fact, carotenoids normally have much less stereoisomers than theoretical number. For example, common cis-lycopenes include 5-cis-, 7-cis-, 9-cis-, 13-cis- and 15-cis-isomers, and cis-β-carotenes include 9-cis-, 13-cis- and 15-cis-isomers.
Natural carotenoids in food (for example, tomato) are dominantly in all-trans-structure, but mainly in cis-configuration in human tissues and cells. Existing study results suggest that carotenoids in cis-configuration, such as cis-lycopenes and cis-β-carotenes, usually have higher biological potency and stronger physiological activity than their all-trans-isomers. In addition, among cis-lycopenes, 5-cis-isomer presents maximal antioxidant activity and stability, and among cis-β-carotenes, 9-cis-isomer has the maximal activity in inhibiting atherosclerosis and reducing incidence of cancers. Therefore, increasing the proportion of cis-configuration in carotenoids, in particularly increasing the proportion of 5-cis-lycopene in lycopenes or 9-cis-β-carotene in β-carotenes, is expected to greatly improve physiological activity of carotenoid products.
Common methods for increasing the proportion of cis-configuration carotenoids using natural carotenoids as raw material include thermal isomerization and photoisomerization.
The thermal isomerization is to promote transformation of all-trans configuration into cis configuration by heating at reflux in an organic phase or by directly heating under special conditions. Patents PCT/EP2007/006747, PCT/EP02/00708, U.S. Pat. No. 7,126,036 and CN101575256 have disclosed a method for preparing cis-lycopenes by heating at reflux in an organic phase, respectively, but these methods have the disadvantages of complicated operation, long processing time and low in 5-cis-lycopene content.
The photoisomerization can be divided into direct photo isomerization and iodine-catalyzed photoisomerization. In direct photoisomerization, groups at a double bond in an active ingredient are subjected to trans-cis configuration transformation in the environment without oxygen, at certain temperature, under light of certain wavelength range. CN101314554 has disclosed a method for preparing cis-lycopene isomers with all-trans-lycopene as raw materials using direct photoisomerization. The photoisomerization has significant drawbacks, such as requiring special reaction apparatus, difficult in expanding reaction scale; As for I2 catalyzed configuration, its disadvantages include the loss of I2 by sublimation and the removal difficulty of I2 after the reaction, so the safety of the product cannot be ensured, and the production cost is inevitably increased.
Nano TiO2 has high chemical and thermal stability, no toxicity and non-mobility and is allowed to contact with food, and therefore has been widely used in the industry of food packing materials. Thus, use of nano TiO2 as support of active iodine is further helpful to meet people's demands on food safety.